SG 38 Zogling - Primary Glider

Hi all, I have decided to have a go at building a Zogling gliding, I think it's other name is the SG38? I think a good span would be 10ft and I have a set of plans that I will scale up . Now looking at the plans the wing section is flat bottomed, but on pictures and video's I have seen of the Zogling (SG38) the wing section looks under-cambered. I wonder if anyone has information as to the actual wing section that the original glider used, as it would be nice to remain on track with regard to scale detail

The main function of primary trainers was to train pilots in the elementary control of gliders and not really designed for much more than short hops and ground slides or delayed plummets down to the bottom of a hill to qualify for the basic certificates. Some limited soaring was possible but the wing section was "built for comfort not speed" so the results of a scale section might be rather limiting even with a fairly large scale model.

There's quite a bit of apparently authentic full size info on this page including a fairly detailed 3 view drawing, if you haven't seen it....

Hi Martin, thanks for your reply, yeah I know it's no floater! I think the glide ratio is 1:10 which is a bit poor when you compare to an ASK 13, which is 28:1 and the high performance glass ships of up to 60:1, but I think it would be a good deal of fun and look the part. I am thinking of using a bungee to launch it to gliding height, obviously an electric motor would spoil the lines. Maybe though an electric motor could be added later if the glide is really dreadful to get some duration flights, who knows. Maybe that's why the airfoil on the plan is flat bottomed for simplicity?. Thanks for the link, I have discovered that link before but thanks anyway.

Thanks for posting links to the plan, guess what, I am using the same plans! how spooky. I noticed though the link to the 'wing' plan does not work, but thanks for posting . My next step (which I began yesterday) is to up scale from the 1/5 scale plansto my 10ft version. I am sure that there are photocopiers out there to do the job but I have undertaken the old task of using a pencil, calculater, ruler and set square to scale her up! So far with a wingspan of 10ft the model looks huge as the chord is 487mm! and the Gottingen section is not thin! Go to do a final check to see if the fuz will fit in the car, the wings should not be a prob as 5ft each. If it is a prob (looks tight) then I could make the fuz join in the centre.

Hi everyone, if you use the plans for the Zogling please note that the wing and the fuz are on two different plans and if you print them out they are different scales. You can also find the plans here

I had to apply different scaling to the wing than to the fuz to get it correct for a 10ft span. My model will turn out to be approx 30% size of original. Here is an example of a 1/3 scale Zogling build on the rc groups website and this will be a valuable resource in building mine.

Here is some background for primaries, Slingsby's T38 used the Kirby kite section (Göttingen 426). Note the rip off cost in 1939 "Slingsby Sailplanes Ltd were offering new gliders from £99. A Kirby Kite 1 cost £159". Considerably less than a kit might be today.

Wiki gives the SG38 wing section as Göttingen 533 and the elevator and rudder as naca0012f60. There's a mention elsewhere of a Göttingen 535 for the wing. Bearing in mind models rarely scale well, it may not matter too much.

Hi Lazygit, many thanks for the info, I think I will go for the Gottingen 533 for the main wing and not the 426 as the pic above shows, so will print off the section at 477 mm chord and post it on the forum to show, like I have done above

Hi Taco, yes that's the tried and trust sandwich method if I'm not mistaken. I had to cut out the lightening holes anyway so thought I would do it this way and it seems to work OK. I have sheeted the inner most ribs (x3) with 1/16 ply, see pic below

The two bottom spars has been spliced and cut to length. The next stage will be to set the airfoil up on blocks as it's an under cambered section this makes it tricky to build. I have cut the blocks out of balsa and they will support the front and back spar off the building board by just the right amount. The trailing edge is just 1/16th sheeting. Got to figure out where to run my wiring for the aileron servos. I think it would be easier than using wires and bell cranks to just put a couple of servo's in the wings. I thought I might hide the cables in in front of the main spars and behind the leading edge, this would require either circular holes of a square hole to be cut in the ribs. The model will be covered in nylon and I won't want to see aileron servo cables through the covering!!!

Rear spar piece that joins onto the back of wing where aileron joins and the corresponding spar (aileron LE) pieces, two per wing. These may need sheeting and some cross members to stiften them up. The wing bit will need shaping /bevelling to allow the aileron to move up and down.

Does anyone know if the Zogling primary glider had any washout incorporated into the wings? Do you think I should incorporate some in anyway? and how much washout is usually acceptable for a glider like this? I don't know what the tip stalling characteristics of this glider were like.